Skip to main content
ESSV Log in
Book my call

Digital signature: what it is, the types and which you need

What an electronic signature is, simple versus advanced versus qualified under eIDAS, what each is worth and how to get a qualified certificate.

Héctor Redondo, CEO and founder of BAI Business CEO and founder of BAI Business

Published on Reviewed on 8 min Regulation

Contents
  1. The three levels, according to the law
  2. What each one is worth
  3. How you get a qualified one
  4. Which one your business needs
  5. Common mistakes
  6. What we have built at BAI
  7. What to do now
  8. Frequently asked questions
  9. Is a simple electronic signature valid?
  10. What is the difference between an advanced and a qualified signature?
  11. What effect does a qualified signature have?
  12. Is it enough to paste an image of my signature into a PDF?
  13. How do I get a qualified signature?
  14. What kind of signature does BAI offer?
  15. How we checked this
  16. Sources
  17. You may also be interested in

> Declaration of interest: BAI Business offers simple electronic signature and publishes this article. It is signed by Héctor Redondo, CEO and founder of BAI Business.

Today I want to talk about the digital signature: what it is, how many kinds there are and which one your business needs so you stop printing, scanning and sending contracts by courier.

First: "digital signature" is a convenient name for three different things. Under European law there is simple, advanced and qualified electronic signature, and they are not worth the same if there is a dispute. For many everyday documents a simple, well-documented signature is enough. For others you need more, and it helps to know when.

The three levels, according to the law

The European eIDAS Regulation (Regulation (EU) 910/2014, Article 3) defines them like this:

Level What it is according to the Regulation
Simple Data in electronic form which is attached to or logically associated with other electronic data and which is used by the signatory to sign (Article 3(10))
Advanced One that meets Article 26: uniquely linked to the signatory; capable of identifying the signatory; created using data that the signatory can, with a high level of confidence, use under their sole control; and linked to the signed data in such a way that any subsequent change is detectable
Qualified An advanced signature created by a qualified signature creation device and based on a qualified certificate for electronic signatures (Article 3(12))

Source: eIDAS Regulation, consolidated text of 18.10.2024 (accessed on 2026-10-10).

What each one is worth

Article 25 of the same Regulation says two important things:

  1. An electronic signature cannot be denied legal effect or admissibility as evidence merely because it is in electronic form or because it does not meet the requirements of a qualified one.
  2. A qualified electronic signature has the equivalent legal effect of a handwritten signature.

Translated: a simple signature counts, but if somebody disputes it, you will have to show that it was that person who signed. That is why the trail matters (who, when, from where, which document). A qualified signature is the equivalent of a handwritten one.

How you get a qualified one

With a qualified certificate issued by a qualified trust service provider. Spain's Law 6/2020, which regulates these services, sets the validity of a qualified certificate at no more than five years (Article 4.2) and requires the holder's identity to be verified: in person or, remotely, by means that give equivalent assurance, such as video identification (Article 7). When you go to request one, the provider will tell you the exact procedure.

Which one your business needs

Imagine a renovation company that closes works quotes with clients: two partners of the client have to accept and one lives in another city. By courier it takes a week. If they sign from their phone with a link that records who signed and when, they sort it out that afternoon. For that kind of quote acceptance, a simple signature with a good trail is usually reasonable. (An invented example, not a real customer; the choice depends on your case.)

My practical rule:

  • Everyday documents (quotes, acceptances, work reports, receipts): a simple signature with a trail.
  • Documents that may end up disputed and are worth a lot of money: consider advanced or qualified.
  • Acts that require a special form (some require a notarised deed): any signature will not do there. Ask your accountant or lawyer.
  • If a rule or a body requires a specific level, that one rules. Ask what the recipient accepts before you choose.
  • Don't ask for more than you need. A qualified signature requires the signatory to have a qualified certificate, which can be a hurdle for a private customer.

This is not legal advice: it is guidance from one business owner to another. If in doubt, consult a lawyer.

Common mistakes

  • Pasting an image of the signature into a PDF. On its own it neither links the signature to the signatory nor makes a later change detectable.
  • Not keeping the evidence. Keep the signed document together with the record of who signed it and when.
  • Not telling the signatory. Tell them which signing method you are going to use and why.
  • Expecting the signature to fix a badly drafted contract. Signing proves the agreement, it doesn't improve it.

What we have built at BAI

At BAI, according to what we publish on the website, each document is produced from a template with the customer's data and your logo, sent for signing to one or several people who sign from their link without printing, and the signed document is saved by itself with the trail of each signature, attached to the customer record. And here is the part I prefer to say plainly: it is a simple electronic signature. If a document requires an advanced or qualified signature, BAI does not present it as such.

The table above works for any tool, and for yours it is worth checking which level it is.

What to do now

Make a list of the documents you sign most each month and mark, next to each, who would dispute them and how much money is at stake. The ones with little money and little dispute are the first you can move to simple signature. If you want to see how we do it, there is documents and digital signature.

Frequently asked questions

Is a simple electronic signature valid?

Article 25(1) of the eIDAS Regulation says an electronic signature shall not be denied legal effect and admissibility as evidence in legal proceedings solely on the grounds that it is in an electronic form or that it does not meet the requirements for qualified electronic signatures (accessed on 2026-10-10).

What is the difference between an advanced and a qualified signature?

The advanced one meets the requirements of Article 26: uniquely linked to the signatory, capable of identifying them, created with data under their sole control and linked to the signed data so that any subsequent change is detectable. The qualified one is an advanced signature created by a qualified device and based on a qualified certificate (Article 3(12)).

What effect does a qualified signature have?

According to Article 25(2) of the eIDAS Regulation, a qualified electronic signature has the equivalent legal effect of a handwritten signature (accessed on 2026-10-10).

Is it enough to paste an image of my signature into a PDF?

On its own it does not guarantee the requirements of the advanced signature, such as linking the signature uniquely to the signatory or making any later change to the document detectable.

How do I get a qualified signature?

With a qualified certificate issued by a qualified trust service provider. Spain's Law 6/2020 sets its validity at no more than five years (Article 4(2)) and requires the holder's identity to be verified, in person or remotely by means that give equivalent assurance, such as video identification (Article 7). The provider tells you the exact procedure.

What kind of signature does BAI offer?

A simple electronic signature, with the trail of each signature. If a document requires an advanced or qualified signature, BAI does not present it as such.

How we checked this

I read the cited articles of the eIDAS Regulation on EUR-Lex and of Law 6/2020 in the BOE on 11 October 2026. This is not legal advice. What I say about BAI comes from the published pages of our website. I wrote it with the help of artificial intelligence from the cited sources and from what we use at BAI; I sign it myself. I took the definitions in Articles 3(10) and 3(12) from the consolidated text of 18.10.2024, read on 10 October 2026.

Sources

You may also be interested in

Regulation

invoicing and payments

Keep reading